This proposal will take advantage of on-going studies in our laboratories that are examining the structure-function relationships of proteins from three groups of viruses: the flaviviruses, the alphaviruses, and the filoviruses. Using information derived from these studies as well as preliminary data previously obtained, we will identify and target specific aspects of the virus replication cycle for the development of inhibitory compounds. The flaviviruses comprise a genus within the family Flaviviridae of plus-strand RNA viruses. Many of its members cause significant disease in humans. Several examples of flaviviruses include dengue, yellow fever, West Nile, and tick-borne encephalitis. We will also carry out studies with the alphaviruses, a genus of plus-strand RNA viruses found in the Togaviridae family. Several examples of alphaviruses are Sindbis and Venezuelan equine encephalitis. In addition, we will examine the major glycoprotein GP1 of Ebola virus using structural and computational approaches and utilize this information to develop antivirals. All three groups of viruses contain members that have been suggested as possible bioterrorism agents. There are few effective vaccines for these viruses and no efficacious antiviral agents. In combination with molecular genetics, our structural studies have suggested possible steps in the virus replication cycle that may be susceptible to inhibition by antivirals. The team of investigators described here brings together diverse experimental strategies that will be brought to bear on the development of antivirals. Richard Kuhn will coordinate the efforts and will be responsible for establishing assays for screening of potential compounds. David Sanders will carry out entry and fusion assays using pseudotyped particles. Michael Rossmann and Janet Smith will carry out X-ray crystallographic studies to examine complexes of viral proteins and bound inhibitors. The design and synthesis of inhibitors will be done by Carol Post, using NMR and molecular dynamic simulations, and Mark Cushman, who will directly synthesize such compounds.